In recent years, as the technique in photographing light-sensitive materials has progressed, high sensitivity light-sensitive materials have been put on the market in sequence. These high sensitivity light-sensitive materials also have made it possible to extend the application of photographing, e.g., to photographing in a dark room without using any strobe light, photographing of sports at a high shutter speed using a telephoto lens, and astronomical photography and other applications requiring a long time of exposure.
In order to provide a high sensitivity light-sensitive material, many efforts have been made. Many studies have been made to improve the shape, formation process, chemical sensitization and spectral sensitization of particulate silver halide, additives and structure of couplers. As a result, some useful inventions have been worked. However, the demand for high sensitivity light-sensitive materials has surpassed the progress of the technique in the art, and these inventions leave to be desired. It has therefore been the industry's usual practice to use particulate silver halide having a larger particle size in combination with other technique to provide a high sensitivity light-sensitive material. However, this practice has a great disadvantage that if a particulate silver halide having a larger size is used, the sensitivity can be raised to some degree but, so long as the silver halide content is kept constant, the number of particles in the silver halide emulsion is decreased and hence the number of development initiating points is decreased, greatly deteriorating the graininess of the light-sensitive material. In order to overcome such a disadvantage, many approaches have been known such as a method as described in British Patent No. 923,045 and JP-B-49-15,495 (the term "JP-B" as used herein means an "examined Japanese patent application") which comprises using a light-sensitive material comprising two or more emulsion layers having the same color-sensitivity and different sensitivities, i.e., different particle sizes of particulate silver halide, a method as described in JP-A55-62,454 (the term "JP-A" as used herein means an "unexamined Japanese patent application") which comprises using a high speed reaction coupler, a method as described in U.S. Pat. Nos. 3,227,554 and 3,632,435 which comprises using a so-called DIR coupler or DIR compound, a method as described in British Patent No. 2,083,640 which comprises using a coupler which produces a mobile dye, and a method as described in JP-A-60-128,443 which comprises using silver halide having a high average silver iodide content. These methods are excellent inventions having great effects. However, these methods leave to be desired with respect to the great demand for high sensitivity and high picture quality. In order to increase the number of development initiating points as much as possible while increasing the particle size of particulate silver halide to be incorporated in the emulsion, the high sensitivity color negative light-sensitive material has been designed to have a more content of particulate silver halide so far as the properties such as desilvering property upon blix permit.
The particulate silver halide to be used herein is normally subjected to chemical sensitization to provide the desired sensitivity and gradation.
The chemical sensitization of silver halide may be accomplished by any suitable known method, such as a sulfur sensitization process using a sulfur-containing compound capable of reacting with silver ion or active gelatin, reduction sensitization process using a reducing substance, noble metal sensitization process using gold or other noble metal compounds or combination thereof. Suitable sulfur sensitizing agents include thiosulfate, thiourea, thiazole and rhodanine. Specific examples of such compounds are described in U.S. Pat. Nos. 1,574,944, 2,410,689, 2,278,947, 2,728,668, 3,656,955, 4,030,928 and 4,067,740. Suitable reduction sensitizing agents include stannous salt, amine salt, hydrazine derivative, formamidinesulfinic acid and silane compound.
Specific examples of such a reduction sensitizing agent are describe in U.S. Pat. Nos. 2,487,850, 2,419,974, 2,518,698, 2,983,609, 2,983,610, 2,694,637, 3,930,867, and 4,054,458.
In order to effect noble metal sensitization, complex salts of the VIII group metal in the periodic complex. Specific examples of such noble metal complexes are described in U.S. Pat. Nos. 2,399,083 and 2,448,060, and British Patent 618,061.
In recent years, a silver halide emulsion having a higher sensitivity has been desired. It has been thought that a chemical sensitization process using a combination of a sulfur sensitizing agent and a noble metal sensitizing agent, particularly a gold-sulfur sensitizing process using a combination of a sulfur sensitizing agent and a gold sensitizing agent is indispensable to accomplish such an object.
In this case, the amount of such a sensitizing agent to be added can be determined by the state of the crystal particulate silver halide to be chemically sensitized (e.g., particle size or its distribution, halogen composition, crystal habit), environmental conditions (e.g., amount and type of binder used, pH, pAg, reaction temperature, reaction time), auxiliary agents for gold sensitization (e.g., accelerator such as thiocyanate or thioether compound, fog inhibitor such as thiosulfonate), and the type of sulfur sensitizing agent and gold sensitizing agent to be used.
A color photographic light-sensitive material normally comprises a silver halide emulsion which has been subjected to chemical sensitization in the manner as described above.
However, it has been found that a color photographic light-sensitive material thus prepared has some disadvantages.
Particularly, some deterioration cause such as an increase in the generation of fog, a reduction in the sensitivity or deterioration in the graininess between the preparation and the use of the light-sensitive material.